Nurseries, garden centres and home gardeners have been commended for their efforts in the fight against myrtle rust disease. As the weather warms up in spring, this serious disease will be on the move again and we must remain vigilant.
Saving our trees
In this winter’s Go Gardening magazine (May 1) we announced that myrtle rust had arrived on Raoul Island, 1000km northeast of the North Island. Mainland New Zealanders were being asked to be on vigilant watch for the serious wind borne disease threatening some of our most precious trees. By the time the magazine was printed a few days later, myrtle rust had been found in Northland.
Early in May New Zealand Plant Producers Incorporated (NZPPI) provided nurseries, transporters and garden centres with guidelines to manage the risk of distributing or becoming infected with myrtle rust. After the first detection of myrtle rust in north Taranaki on May 12, Ministry for Primary Industries (MPI) endorsed those guidelines and praised the nursery industry for its vigilance. Andrew Harrison, chairman of NZPPI called it a “call to arms for our industry”.
Despite those involved doing exactly the right thing, by June 1 we had 32 confirmed myrtle rust finds. The list of infected sites continued to grow and by mid-July, the count of confirmed sightings was up over 90. The majority of these were in private gardens. So far, the most affected species in New Zealand are ramarama and pohutukawa, but other myrtle family members such as manuka and feijoa are still at risk.
Winter has bought scientists a little time. The fungus hibernates in cold temperatures, so even though the weather has been windy, there are few spores produced for spreading. But as the weather warms up the fungus starts releasing a whole new generation of virulent spores, so tiny and light that they are carried long distances on the wind. When they land on a susceptible host they germinate, grow through the leaf tissue and form a network of tiny branches called hyphae, which in turn produce a new crop of spores. Come spring, plant producers and retailers will be at the forefront of the effort to determine exactly where the disease is present and the scale of the outbreak.
Since myrtle rust first appeared in May, the focus of the response has been on aggressive containment and eradication. Growers and retailers who are members of NZPPI are working to strict protocols to ensure the plants arriving in garden centres are highly unlikely to be carrying spores of myrtle rust.
Myrtle rust spores are so tiny and light that they’re carrried long distances by wind.
As time goes on, we are likely to be facing the reality that this disease cannot be eradicated completely and we will have to find ways to minimise its effect. NZPPI and MPI are working closely together on contingency plans to prepare for long term management of myrtle rust.
WHAT IS MYRTLE RUST?
Myrtle rust is a fungal disease native to South America. It is caused by the parasitic fungus Austropuccinia psidii which attacks plants of the myrtle family (myrtaceae).
WHAT DOES MYRTLE RUST LOOK LIKE?
Myrtle rust attacks young, soft, actively growing leaves, shoots and young stems. It is sometimes found in flowers and fruit. Powdery, bright yellow or orange ‘pustules’ are the first symptoms to appear. As the disease progresses the developing lesions may cause a deformation of leaves and shoots, twig dieback and, in severe cases, the death of the entire plant.
HOW DOES MYRTLE RUST SPREAD?
Myrtle rust spores are carried large distances by wind. Spores are also spread by insects and rain splashes, and can be transported on clothing, vehicles or equipment. Early detection is key in preventing its spread.
WHICH PLANTS ARE AFFECTED?
Myrtle rust attacks members of the myrtaceae family, which includes: pohutukawa, manuka, kanuka, ramarama ( Lophomyrtus), gum trees ( Eucalyptus), bottlebrush, peppermint myrtle ( Agonis), feijoa, guava ( Psidium), Chilean guava or ‘NZ cranberry’ ( Myrtus ugni).